Lai Jiangshan discovered a reentrancy issue with markers and fixed it by addingsynchronize_sched() calls at each registration/unregistraiton. It works, but itremoves the ability to do batch registration/unregistration and can causeregistration of ~100 markers to take about 30 seconds on a loaded machine(synchronize_sched() is much slower on such workloads). This patch implements aversion of the fix which won't slow down marker batchregistration/unregistration. It also go back to the original non-synchronizedreg/unreg, and thus needs the followingmarkers-synchronize_marker_unregister.patch patch and friends.